Compilare: user.cpp: In constructor ‘BIT::BIT(std::vector<int>)’: user.cpp:20:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0; i<arr_.size(); i++) { ~^~~~~~~~~~~~ user.cpp: In member function ‘void BIT::update(int, int)’: user.cpp:27:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i < arr.size()) { ~~^~~~~~~~~~~~ user.cpp: In function ‘int op2(BIT&, int)’: user.cpp:88:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (max_stepsize < bit.arr.size()) { ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~ user.cpp:94:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (k + step_size < bit.arr.size() && bit.arr[k + step_size] <= a) { ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~ user.cpp: In function ‘int main()’: user.cpp:108:32: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ("aib.in", "r", stdin); ^ user.cpp:109:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ("aib.out", "w", stdout); ^